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SiO2 xerogel with a large specific surface area
Materials Letters 57 (2003) 2409 – 2412 www.elsevier.com/locate/matlet
Preparation of the SnO2/SiO2 xerogel with a large specific surface area Y.S. Feng *, S.M. Zhou, Y. Li, L.D. Zhang Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, PR China Received 6 August 2002; accepted 10 September 2002
Abstract SnO2/SiO2 nanocomposite xerogel was synthesized by using the about-to-gel silica sol as ‘‘nanoglue’’. Tin oxide uniformly dispersed within the three-dimension network of the silica in the form of nanoparticles. The SnO2/SiO2 nanocomposite xerogel has a large specific surface area (SSA), which depends on the deposition time of the silica sol. D 2002 Elsevier Science B.V. All rights reserved. PACS: 81.05.Ys; 81.20.Ka Keywords: Tin oxide; The SnO2/SiO2 xerogel; Specific surface area; Nanogule
1. Introduction Tin oxide is a kind of wide energy gap semiconductor and has many technological applications in solid-state gas sensors, optical electronic devices, dye-based solar cells and electrodes in thin film [1– 4]. Tin oxide nanoparticles shows size-dependent electronic and optical properties, for example, enhancing the sensitivity to many kinds of gas [5– 7]. On the other hand, owing to their large surface, they have tendency to aggregate and weak thermal stability, which strongly effect their application. In order to overcome this disadvantage, we prepared the SnO2/SiO2 xerogel using the technology analogous
* Corresponding author. Fax: +86-551-5591434. E-mail addresses: [email protected], [email protected] (Y.S. Feng).
to Anderson et al. [8] and Morris et al. [9]. During preparation, the about-to-gel silica solution acted as ‘‘nanogule’’ to build three-dimensional silica network. The xerogel networks play an important role in determining the tin oxide nanocrystalline size, confining their growth and retarding their motion. Tin oxide nanoparticles were dispersed uniformly in xerogel. The obtained xerogel differs from the glassceramic composite prepared in suit by Chiodini et al. [10]. In glass-ceramic composite, the tin oxide nanoparticles were enwrapped by silica, and gas transport paths were interrupted. The measured gas did not react directly with tin oxide surface; the sensitivity of tin oxide nanoparticles may be suppressed. The xerogel composite in this paper remained large specific surface area; tin oxide nanoparticles in mesoporous silica are in contact with atmosphere and presents good sensitivity to reductive gas.
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01245-4
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Y.S. Feng et al. / Materials Letters 57 (2003) 2409–2412
2. Experimental The colloidal suspension of tin oxide nanoparticles was prepared by the method described in Ref. [11]. The colloidal suspension has tin oxide content about 10 wt.%. The silica sol was prepared according to the typical method [12] as follows: tetraethoxysilane (TEOS), alcohol and water (molar ratio TEOS/H2O/ C2H5OH 1:5:10) were mixed under vigorous stirring; aqueous ammonia (20 wt.%) were dropped into the mixed solution to make pH to 9. After stirring 6 h, the solution became transparent, and then was deposited at room temperature for 36 h. The two kinds of the solution were combined and stirred 1 min (molar ratio Sn/Si 10%), then the mixture was poured into a petri dish (A 120 mm) and covered with parafilm. The petri dish was placed into oven at 60 jC for 12 days and 80 jC for 6 days. Finally, the monolithic samples were obtained with the milkiness color. The monolithic samples were annealed firstly at 300 jC for 1 h and then at 600 jC for an hour. The obtained xerogel composite samples (as the SnO2/SiO2 sample) were transparent with colorless. X-ray diffraction (XRD) measurements were carried out on a Philips diffractometer using a PW 1700 goniometer. The transmission electron microscopy (TEM) and high-resolution TEM were carried out on JEOL-2011 spectrograph. Nitrogen sorption isothermal measurement was conducted on an Omnisorp 100CX porosity analyzer. From the sorption data, the specific surface area (SSA) for the obtained samples was evaluated by using the Brunauer –Emmett – Teller equation. The X-ray photoelectron spectroscopy (XPS) was performed on VG ESCALAB MKII instruments.
3. Results and discussion Fig. 1 shows the XRD patterns of the SnO2/SiO2 sample. The peaks are broad and fit well with the previous reported values of the cassieterite SnO2 (JCPDS 1983 41-1445). These indicate tin oxide is formed in the sample with small size. On the other hand, the XRD spectrum does not reveal any other phase except the characteristic peaks of tin oxide. This result evidences that the direct chemical interaction of
Fig. 1. XRD patterns of the SiO2/SnO2 sample.
SnO2 with SiO2 does not occur in the composite xerogel. Fig. 2a shows a bright field TEM micrographs image of the SnO2/SiO2 sample with the selected electron area diffraction (SAED) pattern. Tin oxide presents as slightly elliptical particles uniformly dispersed in the silica xerogel network. Tin oxide nanoparticles are about 5 –7 nm in diameter. The corresponding SAED result also confirms the nanoparticles are cassieterite SnO2 phase. Further information about the SnO2/SiO2 sample is discussed by high-resolution TEM investigation, as shown in Fig. 2b. Tin oxide nanoparticles are surrounded by amorphous silica. Several domains of the lattice are apparent which have spacing of 0.268 nm, corresponding to the (101) face of tin oxide. The nitrogen sorption isotherm measurement shows the SnO2/SiO2 nanocomposite xerogel presents typical IV adsorption and has a large SSA about 516 m2/g. Primary experiment indicates that the SSA of the SnO2/SiO2 sample is effected by the silica deposition time before mixing with the colloidal suspension of tin oxide nanoparticles. The SSA of the SnO2/SiO2 nanocomposite increases from 383 to 516 m2/g by prolonging the silica sol deposition time from 1 to 36 h. To understand the SSA change with the silica sol deposition time, the Si2p XPS was measured (as shown in Fig. 3). For the sample, the silica sol deposited for 1 h, the XPS spectra (Fig. 3a) presented double peaks with Eb = 102.8 and 103.4 eV corresponding to the Si2p of SiOx (x < 2) and
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SiO2, respectively. For the sample, the silica sol deposited 36 h, the XPS spectra (Fig. 3b) presents single peak with Eb = 103.3 eV corresponding to the Si2p of SiO2. Additionally, the gelation time for the mixture solution of the tin oxide colloidal suspension and the silica sol deposited for 36 h is much shorter
Fig. 3. Si2p XPS spectrum of the SnO2/SiO2 sample (a) with silica sol depositing 1 h (curve 1), the spectrum was curve fitted with two Gaussian sum peaks: curve 2 to SiOx (x < 2) and curve 3 to SiO2, (b) with silica sol deposition 36 h.
( < 2 h) than that of the silica sol deposited for 1 h (>12 h). According to the gelation time and the Si2p XPS result, we speculate that the colloidal suspension of tin oxide forbids the silica sol to continue hydrolyze and to condense to form three-dimension networks of silica particles. When silica sol was deposited for 36 h, the silica particle already connected to form networks and the nanocomposite xerogel maintains complete mesoporous constructor.
4. Summary
Fig. 2. (a) Transmission electron micrographs with the selected area electron diffraction (SAED) pattern and (b) high-resolution transmission electron micrographs of the SnO2/SiO2 sample.
We prepared the SnO2/SiO2 nanocomposite xerogel using the about-to-gel silica sol as nanoglue. Tin oxide disperses uniformly within the three-dimension networks of silica particles in the form of the nanoparticles. The silica network played very
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Y.S. Feng et al. / Materials Letters 57 (2003) 2409–2412
important role in determining the tin oxide size, retarding their motion and confining their growth. The obtained SiO2/SnO2 nanocomposite xerogel is in the monolithic form and takes on the large SSA, which is very important for their application especially in the solid-stated gas sensitive field. The formation mechanism and application for SiO2/SnO2 nanocomposite xerogel will be the subject of our future intensive study.
Acknowledgements This project was financially supported by National Natural Science Foundation of China (Grant Number: 10074064).
References [1] O.K. Varghese, L.K. Malhotra, Sens. Actuators, B 53 (1998) 19. [2] N.L. Wu, L.F. Wu, Y.C. Yang, S.J. Huang, J. Mater. Res. 11 (1996) 813.
[3] S. Ferrere, A. Zaban, B.A. Gsegg, J. Phys. Chem., B 53 (1997) 19. [4] J. Zhu, Z.H. Lu, S.T. Aruna, D. Aurbach, A. Gedanken, Chem. Mater. 12 (2000) 2557. [5] G. Gaggiotti, A. Galdikas, S. Kaciulis, G. Mattogno, A. Setkus, J. Appl. Phys. 76 (1994) 4467. [6] C. Xu, T.N. Miura, N. Yamazoe, Sens. Actuators, B 3 (1991) 147. [7] E.R. Leite, I.T. Weber, E. Longo, J.A. Varela, Adv. Mater. 12 (2000) 965. [8] M.L. Anderson, C.A. Morris, R.M. Stroud, C.I. Merzbacher, D.R. Rolison, Langmuir 15 (1999) 674. [9] C.A. Morris, M.L. Anderson, R.M. Stroud, D.R. Rolison, C.I. Merzbacher, D.R. Rolison, Science 284 (1999) 622. [10] N. Chiodini, F. Meinsrd, F. Morazzoni, J. Padovani, A. Paleari, R. Scotti, G. Spinolo, J. Mater. Chem. 11 (2001) 926. [11] C. Goebbert, R. Nonning, M.A. Aegerter, H. Schmidt, Thin Solid Films 351 (1999) 79. [12] R.E. Russo, A.J. Hunt, J. Non-Cryst. Solids 86 (1986) 231.
Preparation of the SnO2/SiO2 xerogel with a large specific surface area Y.S. Feng *, S.M. Zhou, Y. Li, L.D. Zhang Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, PR China Received 6 August 2002; accepted 10 September 2002
Abstract SnO2/SiO2 nanocomposite xerogel was synthesized by using the about-to-gel silica sol as ‘‘nanoglue’’. Tin oxide uniformly dispersed within the three-dimension network of the silica in the form of nanoparticles. The SnO2/SiO2 nanocomposite xerogel has a large specific surface area (SSA), which depends on the deposition time of the silica sol. D 2002 Elsevier Science B.V. All rights reserved. PACS: 81.05.Ys; 81.20.Ka Keywords: Tin oxide; The SnO2/SiO2 xerogel; Specific surface area; Nanogule
1. Introduction Tin oxide is a kind of wide energy gap semiconductor and has many technological applications in solid-state gas sensors, optical electronic devices, dye-based solar cells and electrodes in thin film [1– 4]. Tin oxide nanoparticles shows size-dependent electronic and optical properties, for example, enhancing the sensitivity to many kinds of gas [5– 7]. On the other hand, owing to their large surface, they have tendency to aggregate and weak thermal stability, which strongly effect their application. In order to overcome this disadvantage, we prepared the SnO2/SiO2 xerogel using the technology analogous
* Corresponding author. Fax: +86-551-5591434. E-mail addresses: [email protected], [email protected] (Y.S. Feng).
to Anderson et al. [8] and Morris et al. [9]. During preparation, the about-to-gel silica solution acted as ‘‘nanogule’’ to build three-dimensional silica network. The xerogel networks play an important role in determining the tin oxide nanocrystalline size, confining their growth and retarding their motion. Tin oxide nanoparticles were dispersed uniformly in xerogel. The obtained xerogel differs from the glassceramic composite prepared in suit by Chiodini et al. [10]. In glass-ceramic composite, the tin oxide nanoparticles were enwrapped by silica, and gas transport paths were interrupted. The measured gas did not react directly with tin oxide surface; the sensitivity of tin oxide nanoparticles may be suppressed. The xerogel composite in this paper remained large specific surface area; tin oxide nanoparticles in mesoporous silica are in contact with atmosphere and presents good sensitivity to reductive gas.
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01245-4
2410
Y.S. Feng et al. / Materials Letters 57 (2003) 2409–2412
2. Experimental The colloidal suspension of tin oxide nanoparticles was prepared by the method described in Ref. [11]. The colloidal suspension has tin oxide content about 10 wt.%. The silica sol was prepared according to the typical method [12] as follows: tetraethoxysilane (TEOS), alcohol and water (molar ratio TEOS/H2O/ C2H5OH 1:5:10) were mixed under vigorous stirring; aqueous ammonia (20 wt.%) were dropped into the mixed solution to make pH to 9. After stirring 6 h, the solution became transparent, and then was deposited at room temperature for 36 h. The two kinds of the solution were combined and stirred 1 min (molar ratio Sn/Si 10%), then the mixture was poured into a petri dish (A 120 mm) and covered with parafilm. The petri dish was placed into oven at 60 jC for 12 days and 80 jC for 6 days. Finally, the monolithic samples were obtained with the milkiness color. The monolithic samples were annealed firstly at 300 jC for 1 h and then at 600 jC for an hour. The obtained xerogel composite samples (as the SnO2/SiO2 sample) were transparent with colorless. X-ray diffraction (XRD) measurements were carried out on a Philips diffractometer using a PW 1700 goniometer. The transmission electron microscopy (TEM) and high-resolution TEM were carried out on JEOL-2011 spectrograph. Nitrogen sorption isothermal measurement was conducted on an Omnisorp 100CX porosity analyzer. From the sorption data, the specific surface area (SSA) for the obtained samples was evaluated by using the Brunauer –Emmett – Teller equation. The X-ray photoelectron spectroscopy (XPS) was performed on VG ESCALAB MKII instruments.
3. Results and discussion Fig. 1 shows the XRD patterns of the SnO2/SiO2 sample. The peaks are broad and fit well with the previous reported values of the cassieterite SnO2 (JCPDS 1983 41-1445). These indicate tin oxide is formed in the sample with small size. On the other hand, the XRD spectrum does not reveal any other phase except the characteristic peaks of tin oxide. This result evidences that the direct chemical interaction of
Fig. 1. XRD patterns of the SiO2/SnO2 sample.
SnO2 with SiO2 does not occur in the composite xerogel. Fig. 2a shows a bright field TEM micrographs image of the SnO2/SiO2 sample with the selected electron area diffraction (SAED) pattern. Tin oxide presents as slightly elliptical particles uniformly dispersed in the silica xerogel network. Tin oxide nanoparticles are about 5 –7 nm in diameter. The corresponding SAED result also confirms the nanoparticles are cassieterite SnO2 phase. Further information about the SnO2/SiO2 sample is discussed by high-resolution TEM investigation, as shown in Fig. 2b. Tin oxide nanoparticles are surrounded by amorphous silica. Several domains of the lattice are apparent which have spacing of 0.268 nm, corresponding to the (101) face of tin oxide. The nitrogen sorption isotherm measurement shows the SnO2/SiO2 nanocomposite xerogel presents typical IV adsorption and has a large SSA about 516 m2/g. Primary experiment indicates that the SSA of the SnO2/SiO2 sample is effected by the silica deposition time before mixing with the colloidal suspension of tin oxide nanoparticles. The SSA of the SnO2/SiO2 nanocomposite increases from 383 to 516 m2/g by prolonging the silica sol deposition time from 1 to 36 h. To understand the SSA change with the silica sol deposition time, the Si2p XPS was measured (as shown in Fig. 3). For the sample, the silica sol deposited for 1 h, the XPS spectra (Fig. 3a) presented double peaks with Eb = 102.8 and 103.4 eV corresponding to the Si2p of SiOx (x < 2) and
Y.S. Feng et al. / Materials Letters 57 (2003) 2409–2412
2411
SiO2, respectively. For the sample, the silica sol deposited 36 h, the XPS spectra (Fig. 3b) presents single peak with Eb = 103.3 eV corresponding to the Si2p of SiO2. Additionally, the gelation time for the mixture solution of the tin oxide colloidal suspension and the silica sol deposited for 36 h is much shorter
Fig. 3. Si2p XPS spectrum of the SnO2/SiO2 sample (a) with silica sol depositing 1 h (curve 1), the spectrum was curve fitted with two Gaussian sum peaks: curve 2 to SiOx (x < 2) and curve 3 to SiO2, (b) with silica sol deposition 36 h.
( < 2 h) than that of the silica sol deposited for 1 h (>12 h). According to the gelation time and the Si2p XPS result, we speculate that the colloidal suspension of tin oxide forbids the silica sol to continue hydrolyze and to condense to form three-dimension networks of silica particles. When silica sol was deposited for 36 h, the silica particle already connected to form networks and the nanocomposite xerogel maintains complete mesoporous constructor.
4. Summary
Fig. 2. (a) Transmission electron micrographs with the selected area electron diffraction (SAED) pattern and (b) high-resolution transmission electron micrographs of the SnO2/SiO2 sample.
We prepared the SnO2/SiO2 nanocomposite xerogel using the about-to-gel silica sol as nanoglue. Tin oxide disperses uniformly within the three-dimension networks of silica particles in the form of the nanoparticles. The silica network played very
2412
Y.S. Feng et al. / Materials Letters 57 (2003) 2409–2412
important role in determining the tin oxide size, retarding their motion and confining their growth. The obtained SiO2/SnO2 nanocomposite xerogel is in the monolithic form and takes on the large SSA, which is very important for their application especially in the solid-stated gas sensitive field. The formation mechanism and application for SiO2/SnO2 nanocomposite xerogel will be the subject of our future intensive study.
Acknowledgements This project was financially supported by National Natural Science Foundation of China (Grant Number: 10074064).
References [1] O.K. Varghese, L.K. Malhotra, Sens. Actuators, B 53 (1998) 19. [2] N.L. Wu, L.F. Wu, Y.C. Yang, S.J. Huang, J. Mater. Res. 11 (1996) 813.
[3] S. Ferrere, A. Zaban, B.A. Gsegg, J. Phys. Chem., B 53 (1997) 19. [4] J. Zhu, Z.H. Lu, S.T. Aruna, D. Aurbach, A. Gedanken, Chem. Mater. 12 (2000) 2557. [5] G. Gaggiotti, A. Galdikas, S. Kaciulis, G. Mattogno, A. Setkus, J. Appl. Phys. 76 (1994) 4467. [6] C. Xu, T.N. Miura, N. Yamazoe, Sens. Actuators, B 3 (1991) 147. [7] E.R. Leite, I.T. Weber, E. Longo, J.A. Varela, Adv. Mater. 12 (2000) 965. [8] M.L. Anderson, C.A. Morris, R.M. Stroud, C.I. Merzbacher, D.R. Rolison, Langmuir 15 (1999) 674. [9] C.A. Morris, M.L. Anderson, R.M. Stroud, D.R. Rolison, C.I. Merzbacher, D.R. Rolison, Science 284 (1999) 622. [10] N. Chiodini, F. Meinsrd, F. Morazzoni, J. Padovani, A. Paleari, R. Scotti, G. Spinolo, J. Mater. Chem. 11 (2001) 926. [11] C. Goebbert, R. Nonning, M.A. Aegerter, H. Schmidt, Thin Solid Films 351 (1999) 79. [12] R.E. Russo, A.J. Hunt, J. Non-Cryst. Solids 86 (1986) 231.